Radio receiving system



NOV. 21, 1933. p CRAIG 1,935,738

RADIO RECEIVING SYSTEM Filed Oct. 1, 1929 Palmer H. Crai,

Patented Nov. 21, 1933 UNITED STATES 1,935,738" RADIO RECEIVING SYSTEM Palmer H. Craig,. Cincinnati, Ohio, assignor 'to Invex Corporation, a corporation of New York Application October 1, 1929. Serial No. 396,562

4 Claims.

This invention relates to a radio receiving system, and in particular to the provision of means in a radio receiving system for eliminating or minimizing the eifects' of atmospheric electricity 5 or static.

Operation of my invention is based upon the principle of frequency discrimination between the static and'the desired signal. Investigators have discovered that static impulses are essentially of much longer duration than the period of the carrier wave in the range of ordinary broadcast fre quencies. Thus, the duration of a typical static impulse is from 500 micro-seconds to 2930 microseconds, whereas theiperiod of the carrier wave of broadcast signals (200 to 600 m.) varies from 0.667 micro-seconds to 2 micro-seconds. However, static impulses have superimposed upon their fundamental certain ripples, the average period. of which is approximately 100 micro-seconds (the shortest observed being micro-seconds). Even these, however, are longer than the longest period of the carrier wave of an ordi'nary broadcast signal. For an account of the work of investigators as to the nature of static, 25 reference may be had to a series ofthree papers by Appleton, Watt and Herd, published in Royal Society Proceedings A, volume 103', part I, page 8 1; volume 111-, parts II and III, pages 615-677, and also a paper by Cairns in the Proceedings of the Institute of Radio Engineers, volume 15, page 985.

An object of my invention is to provide a receivingv circuit in which means is provided for discriminating against static impulses to prevent their transmission to the receiving instrument but permitting the transmission of the desired signal wave.

M'yinvention is illustrated in the accompanyingydrawing in which:

Figure 1 illustrates one form of my invention in which I employ a high-pass filter between the antenna and thetuning or selecting circuit, the filter'serving to let through the desired band of wave lengthswhile excluding the static impulses;

Figure 2 is a modification of the arrangement shown in Figure 1;

Figure 3 is a circuit diagram of a second form of my invention in which the static energy is transferred from the antenna to the receiving circuit over two paths with equal intensity and opposite in phase, whereas the signal energy is transferred substantially only over one path; and

Figures 4 and 5 are modifications of. the arrangement shown in Figure 3.

Referring to Figure 1, A indicates an aperiodic antenna circuit connected to a high-pass filter B comprising a network of reiterative series condensers C and shunt inductances D. The output circuit of filter B is connected to the input circuit of an aperiodic amplifier E whose output 5 circuit is coupled to a tunable circuit F included in the input circuit of a vacuum tube detector G. H indicates any suitable signal indicating instrument such as a telephone headset. The filter B is designed in accordance with the principles set out in U. S. patent to Campbell No. 1,227,113, to pass or transmit waves having a frequency above a certain value and to exclude waves or impulses having a frequency below this value. For example, filter B is designed to freely pass all frequencies within the broadcast band, or theband to be received, and the cut-off frequency is adjusted to substantially prevent the transmission of impulses or waves corresponding to the frequency range of static, that is to say, impulses having periods of the order of 30 microseconds and longer. The amplifier E is a unilateral conducting device and is inserted between the filter B and the tuned circuit F to prevent reaction of the tuned circuit upon the so filter B, however, the amplifier may be omitted and tuned circuit F connected directly to' the output of the filter B if desired.

Operation of the arrangement shown in Figure l is as follows: Both static and signal energies are picked up by the antenna circuit A and supplied to the input of the filter B. The signal'frequencies are freely transmitted through the filter, while static impulses having periods 'below vices well known in the art.

It is obvious that filter B may comprise a bandpass filter designed to pass frequencies lying within the tuning range of the selecting circuit F and to keep 'out frequencies both above and below this range.

If desiredan aperiodic amplifier may be inserted between the filter B and the antenna circuit A. Such an amplifier is symbolized by the vacuum tube Ab in Figure 2, and may comprise one or more stages of amplification. The input of the amplifier is connected across a resistance Aa in the aperiodic antenna circuit.

In the arrangement shown in Figure 3 the circuit of antenna 1 includes a coil 2 coupled to corresponding elements are indicated by the same a coil 3, which is included in the input circuit of a detecting unit 4 provided with a signal indicating device 5. The detecting unit 4 may include suitable amplifying and detecting elements. The input circuit of the unit may be tuned by a variable condenser 6 connected across coil 3, or the tuning may be incorporated within the unit itself. A second coil 7 is inductively coupled to coil 2 in the antenna circuit and is connected in circuit with coil 8, which is inductively coupled to coil 3. The circuit between coils 7 and 8 includes a high frequency choke coil 9 designed to effectively choke out signal currents within the tunable range of the receiving system.

Operation of the arrangement shown in Figure 3 is as follows: Both signal and static energies are induced into coils 3 and 7 by coil 2 in the antenna circuit. Due to the presence of choke coil 9, currents of signal frequency will not flow in the circuit including coil 8, but currents due to static impulses will, however, flow in this circuit since the effective frequency of such impulses is lower than the signal frequency. The coupling between coil 8 and coil 3 is adjusted both in magnitude'and direction to cause voltages to be induced in coil 3 equal and opposite to the voltages induced in this coil by static impulses flowing in coil 2. It' will thus be seen that the effect of static impulses upon coil 3 is substantially neutralized by the action of coil 8, and substantially only currents of signal frequency flow in the coil 3 and are effective in operating the detector unit 4.

The arrangement shown in Figure 4 is a modification of the circuit shown in Figure 3, and

reference numerals. In this arrangement the coil 3 is not directly coupled to the antenna circuit, but is indirectly coupled to it by means of a coil 10 inductively coupled to coil 2 In this arrangement coil 8 acts inductively upon coil 3 to effectively neutralize static impulses induced into the input circuit of the detectorby way of coil 10, but currents of signalling frequency induced in coil 10are not neutralized.

. The arrangement shown in Figure 5 isa modification of Figure 3 and of Figure 4. In this case coil 3 is coupled to coil 2 by means of two loop circuits including coils 73 and l0[ll, respectively. One loop circuit includes a low-pass band filter 9a' to exclude a band of frequencies including all frequencies lying within the tuning range of the circuit 36, but passing the lowfrequency static impulses, while the other loop circuit is tuned by series condenser 12 to.

permit the passage of high frequency signaling currents. The two loop circuits are so coupled to coil 3 that static impulses transmitted over the two paths from coil 2 are neutralized in coil 3,

While signal currents transmitted over the loop circuit including coils 10-11 are effective in operating the signal indicating device. The variable condenser 12 may be omitted if desired. v In the arrangements shown in Figs. 3 and 4, instead of employing chokes to exclude the signal wave from the circuit containing coils 7 and 8, a low-pass filter may be employed as in Fig. 5 to exclude the signal wave and let through the static impulses. The relative phase relation of the static impulses transmitted over the two parallel paths may be adjusted by adjustment of the number of sections in the filter.

It is obvious that in anyof the arrangements shown in Figures 3 to 5, an amplifier may be included in the circuit between coil '7 and coil 8. It is also obvious that instead of connecting coil 2 directly in the antenna circuit, it may be included in the output circuit of a non-oscillatory radio frequency amplifier, the input circuit of which includes the antenna circuit. Many other changes in detail arrangement will be apparent to those skilled in the art without departing from my invention in its broadest aspect.

What I claim is:

l. A receiving system comprising a collector circuit, a selector circuit having a definite tuning range, means providing two paths of energy transfer between the collector circuit and the selector circuit, said paths being connected to said selector circuit in opposed relation, and untunecl means in one path to exclude currents of signalling frequency throughout the tuning range of said selector circuit.

2. The method of discriminating between static impulses and signalling currents in radio reception which consists in, collecting both static and signal wave energy, transmitting both static and signal wave energy to a detecting device over one path, transmitting static energy to said detecting device over another path, constantly excluding from said second path signal energy of a band of frequencies including all frequencies lying Within the tuning range of the receiver, and opposing the static energies in said detector device.

M 3. A receiving system comprising a collector circuit, a selector circuit having a definite tuning range, a transmission path connecting said collector circuit with said selector circuit for transrange, a second transmission path connecting collector and selector circuits in opposing relation to said first path, and a low-pass band filter included in said second path for passing static impulses but excluding all signalling currents within the tuning range of said selector circuit.

4. A receiving system comprising a collector circuit, a selector circuit having a definite tunmitting signaling currents within said tuning 1 

